Asamayama

Japan

36.406°N, 138.523°E; summit elev. 2568 m

All times are local (unless otherwise noted)

Asama has been seismically active since 18 September 2000. Heightened seismicity occurred in June 2002, when the daily number of volcanic earthquakes exceeded 300 (BGVN 27:06). The Asama Volcano Observatory (ERI, University of Tokyo) and Japan Meteorological Agency (JMA) reported a new episode of elevated seismicity during 18-19 September 2002 (BGVN 28:04). According to JMA there were brief ash eruptions on 6 February, 30 March, 7 April, and 18 April 2003 to heights of 200-300 m above the crater with minor ashfall around the summit (BGVN 28:04).

Seismic data and plume observations compiled from JMA reports for September 2000 through April 2003 (table 2) reflect this recent activity. White plumes were reported from the Kama-yama crater during every month in this period, with the addition of grayish white plumes on 6 February, 7 April, and 18 April. These white plumes only rose to 1 km or above in April and May 2001, and June and August 2002. In addition, short isolated episodes of volcanic tremor were recorded in October 2001, February 2003, and March 2003. However, 12 episodes occurred in April 2003, with five on the 29th.

Table 2. Summary of seismicity and plume observations at Asama, January 2000-April 2003. All reported plumes originated from the Kama-yama crater, and were described as either white (W) or grayish white (GW). Data courtesy of JMA.

Month

Total volcanic earthquakes

Maximum volcanic earthquakes (date)

Plume Height (m) (date)

Plume Color

Jan 2000

5

1 (4, 5, 9, 14, 18)

300 (25, 26, 28)

W

Feb 2000

3

2 (26)

300 (10)

W

Mar 2000

8

3 (29)

300 (1, 10)

W

Apr 2000

75

27 (17)

400 (17)

W

May 2000

10

2 (19, 27)

500 (5, 30)

W

Jun 2000

26

6 (4)

300 (4, 5, 15)

W

Jul 2000

13

3 (11, 29)

300 (9)

W

Aug 2000

20

3 (5)

200 (2, 21, 26)

W

Sep 2000

419

149 (19)

500 (21)

W

Oct 2000

79

27 (31)

400 (19)

W

Nov 2000

322

34 (25)

300 (4, 6, 23, 27)

W

Dec 2000

234

18 (4, 6)

500 (27)

W

Jan 2001

41

7 (2)

700 (30)

W

Feb 2001

128

46 (19)

500 (15)

W

Mar 2001

162

29 (24)

800 (12, 21, 24)

W

Apr 2001

182

41 (10)

1000 (28)

W

May 2001

20

3 (3, 36)

1200 (17)

W

Jun 2001

11

2 (6, 7)

800 (3)

W

Jul 2001

115

24 (13)

600 (5)

W

Aug 2001

36

5 (18)

400 (13, 28, 29)

W

Sep 2001

99

14 (23)

500 (24, 25)

W

Oct 2001

113

12 (29)

700 (27)

W

Nov 2001

144

13 (9)

600 (11)

W

Dec 2001

80

7 (4)

200 (many)

W

Jan 2002

150

11 (15)

300 (6, 24)

W

Feb 2002

57

5 (many)

400 (24)

W

Mar 2002

732

51 (30)

300 (4, 25)

W

Apr 2002

979

103 (9)

600 (29)

W

May 2002

953

49 (9)

700 (28)

W

Jun 2002

1434

360 (22)

1000 (2, 24)

W

Jul 2002

1499

119 (9)

500 (many)

W

Aug 2002

1464

176 (9)

1500 (6)

W

Sep 2002

1358

243 (18)

600 (19)

W

Oct 2002

837

40 (6)

700 (12)

W

Nov 2002

630

40 (11)

400 (6)

W

Dec 2002

601

58 (22)

300 (23, 26)

W

Jan 2003

775

42 (20)

500 (20, 30)

W

Feb 2003

594

43 (3)

500 (19)

W, GW (6)

Mar 2003

614

41 (15)

300 (20, 30)

W

Apr 2003

458

31 (18)

400 (22)

W, GW (7, 18)

Geologic Background. Asamayama, Honshu's most active volcano, overlooks the resort town of Karuizawa, 140 km NW of Tokyo. The volcano is located at the junction of the Izu-Marianas and NE Japan volcanic arcs. The modern Maekake cone forms the summit and is situated east of the horseshoe-shaped remnant of an older andesitic volcano, Kurofuyama, which was destroyed by a late-Pleistocene landslide about 20,000 years before present (BP). Growth of a dacitic shield volcano was accompanied by pumiceous pyroclastic flows, the largest of which occurred about 14,000-11,000 BP, and by growth of the Ko-Asama-yama lava dome on the east flank. Maekake, capped by the Kamayama pyroclastic cone that forms the present summit, is probably only a few thousand years old and has an historical record dating back at least to the 11th century CE. Maekake has had several major plinian eruptions, the last two of which occurred in 1108 (Asamayama's largest Holocene eruption) and 1783 CE.